Early diagnosis of a disease often increases the likelihood of successful treatment or cure of such disease. Current diagnostic methods, however, depend largely on population-derived average values obtained from healthy individuals. Personalized diagnostic methods are needed that enable the diagnosis, especially the early diagnosis, of the presence of a disease or a condition in individuals who are not known to have the disease or who have recurrent disease. This is of particular importance in cancer.
Leukocytes begin as pluripotent hematopoietic stem cells in the bone marrow and develop along either the myeloid lineage (monocytes, macrophages, neutrophils, eosinophils, and basophils) or the lymphoid lineage (T and B lymphocytes and natural killer cells). The major function of the myeloid lineage cells (e.g., neutrophils and macrophages) is the phagocytosis of infectious organisms, live unwanted damaged cells, senescent and dead cells (apoptotic and necrotic), as well as the clearing of cellular debris. Phagocytes from healthy animals do not replicate and are diploid, i.e., have a DNA content of 2n. On average, each cell contains <10 ng DNA, <20 ng RNA, and <300 ng of protein. Non-phagocytic cells are also diploid and are not involved in the internalization of dead cells or infectious organisms and have a DNA index of one.
The lifetime of various white blood cell subpopulations varies from a few days (e.g., neutrophils) to several months (e.g., macrophages). Like other cell types, leukocytes age and eventually die. During their aging process, human blood- and tissue-derived phagocytes (e.g., neutrophils) exhibit all the classic markers of programmed cell death (i.e., apoptosis), including caspase activation, pyknotic nuclei, and chromatin fragmentation. These cells also display a number of “eat-me” flags (e.g., phosphatidylserine, sugars) on the extracellular surfaces of their plasma membranes. Consequently, dying and dead cells and subcellular fragments thereof are cleared from tissues and blood by other phagocytic cells.
One object of the present invention is to provide diagnostic methods that can facilitate the detection of cancer markers, e.g., nucleic acids, proteins, and the like by using phagocytic cells alone, or in combination with non-phagocytic cells. Another object of this invention is to provide methods of identifying cancer markers and further use such markers alone or together with any known markers to diagnose cancer.